1. Field of the Invention
The present invention relates to a mark position detecting apparatus and a mark position detecting method to be adopted in the detection of the position of a inspection mark on a substrate and, more specifically, it relates to a mark position detecting apparatus and a mark position detecting method ideal for a highly accurate position detection which may be performed during the process of manufacturing semiconductor elements or the like.
2. Description of the Related Art
As is known in the related art, when manufacturing a semiconductor element or a liquid crystal display element, a circuit pattern (resist pattern) is transferred onto a resist film through an exposure step during which the circuit pattern formed at a mask (reticle) is imprinted on the resist film and a development step during which exposed portions or unexposed portions of the resist film are dissolved. Then, by performing etching, vapor deposition or the like with the resist pattern acting as a mask (processing step), the circuit pattern is transferred onto a film constituted of a specific material set below adjacent to the resist film (pattern formation process).
Next, a similar pattern formation process is repeated in order to form another circuit pattern over the circuit pattern formed at the film constituted of the specific material. By repeatedly executing the pattern formation process numerous times, circuit patterns transferred onto films constituted of various materials are laminated on the substrate (a semiconductor wafer or a liquid crystal substrate), and thus, a semiconductor element circuit or a liquid crystal display element circuit is formed.
During the manufacturing process described above, the mask and the substrate are aligned with each other prior to the exposure step in each pattern formation process so as to ensure that the circuit patterns at the films constituted of various materials are registered with precise alignment. In addition, the state of the registration of the resist pattern on the substrate is inspected after the development step and prior to the processing step so as to improve the product yield.
It is to be noted that during the alignment of the mask and the substrate (executed prior to the exposure step), the circuit pattern on the mask and the circuit pattern formed on the substrate through the immediately preceding pattern formation process are aligned with each other. This alignment is executed by using alignment marks indicating reference positions of the individual circuit patterns.
In addition, during the inspection of the state of the registration of the resist pattern on the substrate (executed prior to the processing step), the state of registration of the resist pattern relative to the circuit pattern formed through the immediately preceding pattern formation process (hereafter referred to as a “base pattern”) is inspected. This registration state inspection is executed by using registration marks indicating reference positions of the base pattern and the resist pattern.
The position of such an alignment mark or registration mark (collectively referred to as a “inspection mark”) is detected based upon the brightness distribution of image signals obtained by positioning the inspection mark within the visual field range of the apparatus and capturing the reflected image of the inspection mark with an image-capturing element such as a CCD camera. The brightness distribution in the image signals is constituted of brightness information provided in units of the individual pixels at the image-capturing surface of the image-capturing element.
In the related art described above, the position of the inspection mark is detected based upon the brightness distribution in the image signals provided by the image-capturing element and also, a registration measurement value is obtained through measurement. However, there is a problem with the related art technology in that the results of the positional detection and the results of the measurement of the registration measurement value fluctuate depending upon the actual positioning point of the inspection mark within the visual field range of the apparatus. This leads to a concern for low repeatability in that matching results cannot be achieved from a positional detection and a registration measurement executed for a given inspection mark if the positioning point for the inspection mark within the visual field range is not consistent.
The phenomenon is considered to be attributable to fixed pattern noise from optical systems or the image-capturing element remaining in the image signals. The problem discussed above has become more prevalent as inspection marks with a smaller stage height have become increasingly common in recent years, since the contrast of the brightness distribution in image signals obtained from a inspection mark with a reduced stage height is lower and is more likely to be affected by the fixed pattern noise.